Zirconium metal has historically been a material of construction, in particular cladding for fuel rods, for nuclear reactors, and there has been a continuing interest in reducing its tendency to adsorb thermal neutrons. The more transparent the internal materials of construction of a nuclear reactor are to such thermal neutrons the more efficiently the reactor will function since a certain number of these neutrons are necessary to sustain the nuclear reaction and their production must compensate for the adsorption by the internal materials of construction. Early efforts were directed to separating zirconium from hafnium. The two elements occur together naturally but the hafnium has a substantially larger capture section for thermal neutrons. Such efforts involved both chromatographic techniques using an ion exchange resin and various solvent extraction techniques.
Recent efforts have been directed to isolating a zirconium isotope with either a particularly high or a particularly low cross section to thermal neutrons. This allows the production of a zirconium with a lower average cross section than one composed of the naturally occurring isotope distribution. These efforts at isomer separation have generally involved some type of solvent extraction. These separation techniques are generally only able to separate one isomer at a time. Thus they do not provide a means for simultaneously isolating the zirconium 90 and 94 isotopes which are recognized as having particularly small cross sections (one source lists them as 0.055 and 0.031 Barns, respectively, as compared to 0.567 Barns for zirconium 91 and 0.1430 for zirconium 92).
More recently, it has been proposed that isotopes of zirconium could be separated in an economically practical manner by the use of continuous steady state chromatography utilizing a cation exchange resin as the stationary phase. The preferred stationary phase in this proposal was sulfonated crosslinked polystyrene beads. It appears that this proposal provides a continuous process for isolating both of the abundant low thermal cross section isotopes, zirconium 90 and zirconium 94, in a single procedure.
It is an object of the present invention to provide an improved process for chromatographically separating the isotopes of zirconium. It is a further object of the present invention to provide a process which facilitates the recycle of the eluant. It is an additional object to provide a process which facilitates the concentration of heavy metal waste and radiochemical waste and also facilitates the separation of these two types of waste from each other. Another object of the present invention is to provide a process which facilitates converting the high thermal neutron capture cross section isotopes to high quality ceramic material.